Meltblown filter medium

ABSTRACT

Filter media, as well as related assemblies, systems and methods. Filter media may contain one or more layers formed of a meltblown material.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.12/266,892, filed Nov. 7, 2008, which claims priority under 35 U.S.C.§119(e)(1) to U.S. Provisional Patent Application Ser. No. 60/986,642,filed Nov. 9, 2007, both which are incorporated herein by reference intheir entireties.

FIELD

The disclosure generally relates to filter media, as well as relatedassemblies, systems and methods.

BACKGROUND

Filter media are used in a variety of systems. The media are typicallyused to remove undesirable materials (e.g., particles) from a liquid orgas by passing the liquid or gas through the media.

SUMMARY

The disclosure generally relates to filter media, as well as relatedassemblies, systems and methods.

In one aspect, the disclosure features an article that includes first,second and third layers. The second layer includes a meltblown material.The third layer includes an adhesive and is between the first and secondlayers.

In another aspect, the disclosure features an article that includes afirst layer, a second layer and a third layer. Optionally, the thirdlayer can be a scrim. The second layer includes a meltblown material.The scrim is between the first and second layers, or the second layer isbetween the first layer and the scrim.

In a further aspect, the disclosure features an article that includesfirst, second and third layers. The second layer includes a meltblownmaterial, and the third layer is between the first and second layers.The article is a filter medium.

In an additional aspect, the disclosure features an assembly thatincludes a housing and a filter medium supported by the housing. Thefilter medium can be, for example, any of the articles described in thepreceding three paragraphs.

In yet another aspect, the disclosure features a filter medium having aninitial dust capture efficiency of at least 90%, and a dust holdingcapacity of at least 50 g/m².

In still another aspect, the disclosure features a filter medium havinga periodic dust capture efficiency of at least 90%, and a dust holdingcapacity of at least 50 g/m².

In another aspect, the disclosure features a filter medium having aninitial cleanability test time of at least four hours.

In a further aspect, the disclosure features a filter medium having asoot particle capture efficiency of at least 80%.

In an additional aspect, the disclosure features a filter medium havinga NaCl particle filtration efficiency of at least 30% and a NaClparticle capture test time of at least 40 minutes.

In yet a further aspect, the disclosure features a filter medium havinga liquid filtration efficiency of at least 45%.

In still another aspect, the disclosure features a method that includesforming any of the articles and/or filter media described in thepreceding paragraphs of summary.

In another aspect, the disclosure features a method that includesadhering a meltblown material to an article comprising a substrate toprovide a filter medium.

In an additional aspect, the disclosure features a method that includessupporting a meltblown material with a scrim to provide a first article,and bonding the first article and a substrate together to provide afilter medium.

In a further aspect, the disclosure features a filter medium thatincludes first and second layers. The second layer may be different fromthe first layer. The second layer includes a first meltblown material.The first layer can be, for example, a meltblown material or anelectrospun material. In some embodiments, the first and second layersare supported by another layer.

In another aspect, the disclosure features a filter medium that includesfirst, second and third layers. The second layer includes a plurality offibers, and the second layer has a thickness of at least five microns.The third layer includes a scrim or an adhesive material.

In yet another aspect, the disclosure features any of the articlesand/or filter media described in the preceding paragraphs of thesummary, with an aged cleanability test time that is at least 70% of theinitial cleanability test time.

In still another aspect, the disclosure features a filter medium havingaged cleanability test time that is at least 70% of the initialcleanability test time.

In an additional aspect, the disclosure features an article or filtermedium as described in any of the preceding paragraphs of the summary,with a liquid filtration retention efficiency of at least 60%.

In a further aspect, the disclosure features a filter medium having aliquid filtration retention efficiency of at least 60%.

In an additional aspect, the disclosure features an article thatincludes a substrate and a meltblown material bonded to the substrate.

In another aspect, the disclosure features a meltblown layer having aplurality of crests and valleys, a distance between adjacent valleysbeing at least 400 microns.

In yet another aspect, the disclosure features an article that includesa first layer and a second layer bonded to the first layer, the secondlayer comprising fibers having an average diameter of at most 1.5microns.

In one aspect, the disclosure feature an article that includes a firstlayer having first and second sides; a second layer comprising ameltblown material; and a material between the first side of the firstlayer and the second layer. The article has a corrugation channel widthof at least 150 mils, a corrugation depth of at least 8 mils on thefirst side of the first layer, and a corrugation depth of at least 8mils on the second side of the first layer.

In another aspect, the disclosure features an article that includes afirst layer having first and second sides; a second layer comprisingfibers; and a material between the first side of the first layer and thesecond layer. At least 5% of the fibers in the second layer extend adistance of at least 0.3 micron in a direction substantiallyperpendicular to a surface of the second layer. The article has acorrugation channel width of at least 150 mils, a corrugation depth ofat least 8 mils on the first side of the first layer, and a corrugationdepth of at least 8 mils on the second side of the first layer.

In a further aspect, the disclosure features an article that includes afirst layer having first and second sides; a second layer comprisingfibers having a fiber diameter geometric standard deviation of greaterthan 1.3; and a material between the first side of the first layer andthe second layer. The article has a corrugation channel width of atleast 150 mils, a corrugation depth of at least 8 mils on the first sideof the first layer, and a corrugation depth of at least 8 mils on thesecond side of the first layer.

In an additional aspect, the disclosure features a first layer havingfirst and second sides; a second layer comprising a meltblown material;and a material between the first side of the first layer and the secondlayer. The article is a corrugated article having a retained corrugationof at least 25%.

In one aspect, the disclosure features an article that includes a firstlayer having first and second sides; a second layer comprising fibers,at least 5% of the fibers in the second layer extending a distance of atleast 0.3 micron in a direction substantially perpendicular to a surfaceof the second layer; and a material between the first side of the firstlayer and the second layer. The article is a corrugated article having aretained corrugation of at least 25%.

In another aspect, the disclosure features an article that includes afirst layer having first and second sides; a second layer comprisingfibers having a fiber diameter geometric standard deviation of greaterthan 1.3; and a material between the first side of the first layer andthe second layer. The article is a corrugated article having a retainedcorrugation of at least 25%.

In a further aspect, the disclosure features a article that includes afirst layer; a second layer comprising a meltblown material; and anadhesive material between the first and second layers. The adhesivematerial is present in at least 70% of the area between the first andsecond layers.

In an additional aspect, the disclosure features an article thatincludes a first layer; a second layer comprising fibers; and anadhesive material between the first and second layers. The adhesivematerial is present in at least 70% of the area between the first andsecond layers, and at least 5% of the fibers in the second layer extenda distance of at least 0.3 micron in a direction substantiallyperpendicular to a surface of the second layer.

In one aspect, the disclosure features an article that includes a firstlayer; a second layer comprising fibers; and an adhesive materialbetween the first and second layers. The adhesive material is present inat least 70% of the area between the first and second layers, and thefibers in the second layer have a fiber diameter geometric standarddeviation of greater than 1.3.

In another aspect, the disclosure features an article that includes afirst layer; a second layer comprising a meltblown material; and anadhesive material between the first and second layers. The mean peelstrength between the first and second layers is at least 0.5 ounce perinch.

In a further aspect, the disclosure features an article that includes afirst layer; a second layer comprising fibers, at least 5% of the fibersin the second layer extending a distance of at least 0.3 micron in adirection substantially perpendicular to a surface of the second layer;and an adhesive material between the first and second layers. The meanpeel strength between the first and second layers is at least 0.5 ounceper inch.

In an additional aspect, the disclosure features an article thatincludes a first layer; a second layer comprising fibers having a fiberdiameter geometric standard deviation of greater than 1.3; and anadhesive material between the first and second layers. The mean peelstrength between the first and second layers is at least 0.5 ounce perinch.

In one aspect, the disclosure features an article that includes a firstlayer; a second layer comprising a meltblown material; and an adhesivematerial between the first and second layers. The adhesive material hasan open time of at least 15 seconds.

In another aspect, the disclosure features an article that includes afirst layer; a second layer comprising fibers; and an adhesive materialbetween the first and second layers. The adhesive material has an opentime of at least 15 seconds, and at least 5% of the fibers in the secondlayer extend a distance of at least 0.3 micron in a directionsubstantially perpendicular to a surface of the second layer.

In a further aspect, the disclosure features an article that includes afirst layer; a second layer comprising fibers; and an adhesive materialbetween the first and second layers. The adhesive material has an opentime of at least 15 seconds, and the fibers in the second layer have ageometric standard deviation of greater than 1.3.

In an additional aspect, the disclosure features an article thatincludes a first layer, and a second layer comprising a meltblownmaterial. The article has a Beta decay of at most 20% at a particle sizeof four microns.

In yet another aspect, the disclosure features a method that includesusing a pressure of from 20 pounds per linear inch to 40 pounds perlinear inch to adhere a meltblown material to an article comprising asubstrate to provide a filter medium.

Embodiments may exhibit one or more of the following advantages.

Embodiments may provide one or more of the following advantages. Incertain embodiments, the filter medium can be relatively durable,relatively good at capturing fine particles, relatively good at holdingmaterial (e.g., dust), exhibit relatively good cleanability, relativelygood soot capture, and/or relatively good liquid filtration. In someembodiments, the filter medium can simultaneously exhibit advantagesthat are typically not simultaneously provided by at least some knownfilter media. As an example, in certain embodiments, the filter mediumcan be effective at capturing fine particles while also being relativelydurable. As another example, in some embodiments, the filter mediumefficiently captures particles while also having a good ability to holdmaterials (e.g., dust). As a further example, in certain embodiments,the filter medium can exhibit increased particle capture efficiencywhile maintaining or increasing particle capture capacity. In certainembodiments, the filter medium, as well as related filter systems, canbe prepared in a relatively quick, inexpensive and/or simple manner. Insome embodiments, the processes disclosed herein can be used to providea corrugated article (e.g., corrugated filter medium) that has goodcorrugation properties. As an example, a corrugated article can includea substrate (that is corrugated as provided) having an adhesive andadditional layer disposed thereon, whereon the corrugation properties(e.g., corrugation depth) of the final article is not substantiallydifferent from the corrugation depth of the substrate as provided priorto having the adhesive and additional layers disposed thereon. As ananother example, a corrugated article can include a substrate (that iscorrugated as provided) having an adhesive and additional layer disposedthereon, whereon the corrugation properties (e.g., corrugation depth) ofthe side of the article having the adhesive and additional layer are notsubstantially different from the corrugation depth of the other side ofthe article.

BRIEF DESCRIPTION OF THE FIGURES

The disclosure may be better understood based on the description belowas well as the figures, in which:

FIG. 1 is a cross-sectional view of a filter medium;

FIG. 2 is a cross-sectional view of a pleated filter medium;

FIG. 3 is partial cut-away perspective view of a filter assemblyincluding a filter medium;

FIG. 4 is a cross-sectional view of a corrugated filter medium;

FIG. 5 is schematic view of a system configured to be used in themanufacture of a filter medium;

FIG. 6 is a cross-sectional view of a meltblown layer; and

FIG. 7 is a schematic view of a system configured to be in themanufacture of a filter medium.

DETAILED DESCRIPTION

The disclosure generally relates to filter media, as well as relatedassemblies, systems and methods. FIG. 1 is a cross-sectional view of anexemplary filter medium 10 that includes a substrate 12, an intermediatelayer 14 and a meltblown layer 16. FIG. 2 depicts a typical pleatedconfiguration of filter medium 10. FIG. 3 shows a cut-away perspectiveof an exemplary filter assembly 100 including a filter housing 101, afilter cartridge 102, an inner screen 108 and an outer screen 103.Filter medium 10 is disposed in filter cartridge 102. During use, a gasenters assembly 100 via an opening 104 and then passes through innerscreen 108, filter medium 10 and outer screen 103. The gas then exitsfilter assembly 100 via opening 106.

I. FILTER MEDIUM

A. Substrate

Substrate 12 is generally used to provide mechanical integrity to filtermedium 10.

Substrate 12 can be formed from one or more layers of material. Examplesof materials include glasses, celluloses, synthetic materials, ceramics,polymers, cotton, hemp, carbon and metals. Typically, substrate 12includes fibers of one or more materials. Exemplary classes of fibersinclude natural fibers, organic fibers and inorganic fibers.Combinations of fibers and/or materials can be used. In certainembodiments, substrate 12 may include one or more layers that do notcontain fibers. Examples of non-fibrous materials that may be used insubstrate 12 include open cell foam structures. Open cell foamstructures can, for example, be made of polymers, such as polyolefinsand polystyrenes.

Substrate 12 may be made using any suitable method. In some embodiments,substrate 12 is made by a method that includes web forming (e.g., wetlaid, dry laid, direct laid), carding, spun bonding, melt blowing andfilm fibrillation. The particular configuration of the substrate candepend on the intended application of the filter media, and theparticular configuration can be varied to achieve the desired structuralproperties, including stiffness, strength, pleatability, temperatureresistance. As an example, when filter medium 10 is designed for use inheavy duty air filtration systems, gas turbine filtration systems,automotive air filtration systems, and/or pulse cleaning applications,substrate 12 may be a wet-laid paper, such as cellulose or asynthetic/cellulose blend. As another example, when filter medium 10 isdesigned for use in HVAC filtration systems, liquid filtration systems,HEPA filtration systems, and/or battery separators, substrate 12 may bea wet-laid paper (e.g., made from cellulose, glass and/or syntheticfibers), carded nonwovens, spunbonds, meltblowns, or air laid (e.g.,synthetic or cellulose).

In general, substrate 12 may have any desired thickness. Typically,substrate 12 is at least 200 microns (e.g., 300 microns, 400 microns,500 microns, 600 microns) thick, and/or at most 1500 microns (e.g., 1400microns, 1300 microns, 1200 microns, 1100 microns, 1000 microns) thick.In some embodiments, substrate 12 has a thickness of from 200 microns to1500 microns (e.g., 200 microns to 1000 microns, 400 microns to 1000microns). As referred to herein, the thickness of substrate 12 isdetermined according to TAPPI T411.

The basis weight of substrate 12 is usually selected so that substrate12 provides a desired amount of mechanical integrity to filter medium10. In certain embodiments, substrate 12 has a basis weight of at least25 g/m² (e.g., 50 g/m², 75 g/m²), and/or at most 250 g/m² (e.g. 200g/m², 150 g/m²). For example, in some embodiments, substrate 12 has abasis weight of from 25 g/m² to 200 g/m² (e.g., from 50 g/m² to 200g/m², from 75 g/m² to 150 g/m²). As referred to herein, basis weight isdetermined according to ASTM D-846.

Substrate 12 can be designed to have any desired air permeability. Insome embodiments, substrate 12 has an air permeability of at least threecubic feet per minute (CFM) (e.g., 10 CFM, 25 CFM), and/or at most 400CFM (e.g., 300 CFM, 200 CFM, 150 CFM, 100 CFM). As an example, incertain embodiments, substrate 12 has an air permeability of from twoCFM to 400 CFM (e.g., from 10 CFM to 300 CFM, from 25 CFM to 200 CFM).As used herein, air permeability is determined at a pressure of 0.5 inchwater column according to ASTM F778-88.

Substrate 12 can also be designed to have any desired filtrationefficiency. In certain embodiments, substrate 12 has a NaCl particlefiltration efficiency (measured with flow rate of 32 liters per minute)of less than 10% (e.g., less than 8%, less than 5%) (see discussionbelow regarding the test for NaCl particle filtration efficiency).

While shown in FIG. 1 as being continuous, in some embodiments,substrate 12 can be discontinuous. For example, substrate 12 could beformed of filaments (yarns) which themselves could be continuous ordiscontinuous. Additionally or alternatively, substrate 12 could be inthe form of a material with holes in it (e.g., in the form of a mesh).Additionally or alternatively, substrate 12 could be in the form ofpatches (e.g., dots) of material.

B. Intermediate Layer

1. Adhesive

In some embodiments, layer 14 is formed of an adhesive (e.g., a hot meltadhesive, a pressure sensitive adhesive, a thermoplastic adhesive, athermoset adhesive) that is adhered to layers 12 and 16. Generally, theadhesive is a polymer. Examples of polymers include ethylene vinylacetate copolymers, polyolefins (e.g., polyethylenes, polypropylenes,amorphous polyolefin), polyamides (e.g., nylons), epoxies,cyanoacrylates, polyurethanes (e.g., moisture cured polyurethanes) andpolyesters. In some embodiments, the adhesive is an ethylene vinylacetate copolymer. Examples of commercially available materials includeamorphous polyolefin adhesives available from Bostik (Wauwatosa, Wis.)under tradenames HM 4379, M2751 and H3199, and from Heartland(Germantown, Wis.) under tradename H312. Examples of commerciallyavailable materials also include copolyesters available from Bostik(Wauwatosa, Wis.) under tradenames HM4199, HM4156 and Vitel 4361B.Examples of commercially available materials further include polyamidesavailable from Bostik (Wauwatosa, Wis.) under tradenames HM 4289LV andHM4229.

In some embodiments, layer 14 if formed of a web of fibers less than 4micron in diameter with a geometric standard deviation of 1.4

The thickness of adhesive layer 14 can generally be selected as desired.In some embodiments, the thickness of adhesive layer 14 is at least fivemicrons (e.g., at least 10 microns, at least 25 microns), and/or at most100 microns (e.g., at most 75 microns, at most 50 microns). For example,the thickness of adhesive layer 14 can be from five microns to 100microns (e.g., from five microns to 75 microns, from five microns to 50microns) as determined by scanning electron microscopy.

In general, the basis weight of adhesive layer 14 can be selected asdesired. In some embodiments, adhesive layer 14 has a basis weight of atmost 10 g/m² (at most 8 g/m², at most 5 g/m²), and/or at least 0.5 g/m²(e.g., at least 1 g/m², at least 2 g/m²). For example, in someembodiments, adhesive layer 14 can have a basis weight of from 0.5 g/m²to 10 g/m² (e.g., from 1 g/m² to 8 g/m², from 2 g/m² to 5 g/m²).

While shown in FIG. 1 as being continuous, in some embodiments, adhesive14 can be discontinuous. For example, adhesive 14 could be in the form amaterial with holes in it (e.g., in the form of a mesh). Additionally oralternatively, adhesive 14 could be in the form of patches (e.g., dots)of material. Typically, the amount of adhesive 14 between layers 12 and16 is sufficient to provide appropriate adhesion between layers 12 and16 when considering the intended use of article 10. For example, in someembodiments, adhesive 14 is present in at least 70% (e.g., at least 75%,at least 80%, at least 85%, at least 90%, at least 95%, at least 99%,100%) of the area between layers 12 and 14. In general, adhesive 14 isselected to such that the mean peel strength between layers 12 and 16 isat least 0.5 ounce per inch of width (e.g., at least one ounce per inchof width, at least 1.5 ounces per inch of width). In some embodiments,adhesive 14 is selected so that the mean peel strength between layers 12and 16 is at most four ounces per inch of width. As used herein, the“mean peel strength” of a first layer/adhesive/second layerconfiguration is determined as follows. The test is a modified versionof ASTM D903, using a Thwing-Albert Intellect II tensile tester. Samplesare cut to two inches by seven inches coupons, and the peeling is donein the machine direction. TUFFLEX (TF4150 85447) tape from IntertapeInc. (Montreal, Quebec, Canada) is applied to the length of the coatedsurface of the specimen to firmly bond to the top layer to be able toseparate the laminate. A half inch prepeel is used to start thedelamination. The tester cross head and top air grip moves at a speed 12inches per minute from the stationary bottom air grip. The test iscomplete when the cross-head and the top air grip moves four inches fromthe initial position. The maximum peel strength and minimum peelstrength are recorded as a function of the load measured by the loadcell. The mean peel strength is calculated from the loads measured bythe load cell during the entirety of the test. All peel strengths aredivided in half to report a peel strength per inch width by dividing bytwo.

Generally, adhesive 14 is selected to have an appropriate open time forthe manufacturing process below. For example, the open time of adhesive14 should be sufficient so that it does not become non-adhesive betweenthe time it is applied to one layer (e.g., layer 12 or layer 16) and thetime adhesive 14 contacts the other layer (e.g., layer 16 or layer 12).In some embodiments, adhesive 14 has an open time of at least 15 seconds(e.g., at least 20 seconds, at least 30 seconds at least 40 seconds). Incertain embodiments, layer 14 has an open time of at most 60 seconds. Asused herein, the “open time” of an adhesive is determined according toASTM D4497 using a 1/16 inch wide bead of adhesive.

2. Scrim

In some embodiments, layer 14 serves as a carrier layer (scrim) formeltblown layer 16 (see process discussion below). In such embodiments,scrim 14 is typically bonded together with layers 12 and 16 (e.g.,laminated together).

Scrim 14 can be, for example, formed of a polymer. Examples of polymersinclude polyesters, polyamides and polyolefins. Optionally, scrim 14 isformed of a spunbond nonwoven material or a carded nonwoven material. Insome embodiments, scrim 14 is formed of a spunbond polypropylene.

Generally, the thickness of scrim 14 can be selected as desired. Incertain embodiments, scrim 14 is at least 50 microns (e.g., at least 100microns, at least 200 microns) thick, and/or at most 1000 microns (e.g.,900 microns, 750 microns) thick. For example, the thickness of scrim 14can be from 50 microns to 1000 microns (e.g. from 100 microns to 900microns, from 250 microns to 750 microns) thick. As referred to herein,the thickness of scrim 14 is determined according to TAPPI T411.

In general, the basis weight of scrim 14 can be selected as desired. Insome embodiments, adhesive layer 14 has a basis weight of at most 100g/m² (at most 90 g/m², at most 75 g/m²), and/or at least five g/m²(e.g., at least 10 g/m², at least 20 g/m²). For example, in someembodiments, adhesive layer 14 can have a basis weight of from five g/m²to 100 g/m² (e.g., from five g/m² to 90 g/m², from five g/m² to 75g/m²).

While shown in FIG. 1 as being continuous, in some embodiments, scrim 14can be discontinuous. For example, scrim 14 could be in the form amaterial with holes in it (e.g., in the form of a mesh). Additionally oralternatively, scrim 14 could be in the form of patches (e.g., dots) ofmaterial.

C. Meltblown Layer

Layer 16 is formed via meltblown process, as discussed below. Ingeneral, layer 16 is formed of fibers having an average diameter of atmost 1.5 microns (e.g., at most 1.4 microns, at most 1.3 microns, atmost 1.2 microns, at most 1.1 microns, at most one micron), and/or atleast 0.2 micron (e.g., at least 0.3 micron, at least 0.4 micron, atleast 0.5 micron), as measured using scanning electron microscopy. As anexample, in some embodiments, layer 16 is formed of fibers having anaverage diameter of from 0.2 micron to 1.5 microns (e.g., from 0.3microns to 1.4 microns, from 0.4 micron to 1.3 microns). As anotherexample, in certain embodiments, layer 16 is formed of fibers having anaverage diameter of from 0.2 micron to 0.5 micron (e.g., from 0.3 micronto 0.5 micron, from 0.4 micron to 0.5 micron, from 0.2 micron to 0.4micron, from 0.2 micron to 0.3 micron, from 0.3 micron to 0.4 micron).In general, at least 5% (e.g., at least 10%, at least 25%, at least 50%,at least 60%, at least 75%) of the fibers in the meltblown materialextend a distance of at least 0.3 micron in a direction substantiallyperpendicular to a surface of the second layer as indicated by the arrowin FIG. 1.

Typically, the meltblown material is formed of one or more polymers.Exemplary polymers include polyolefins (e.g., polypropylenes),polyesters (e.g., polybutylene terephthalate, polybutylene naphthalate),polyamides (e.g., nylons), polycarbonates, polyphenylene sulfides,polystyrenes, polyurethanes (e.g., thermoplastic polyurethanes).Optionally, the polymer(s) may contain fluorine atoms. Examples of suchpolymers include PVDF and PTFE.

Layer 16 can generally have any desired thickness. In some embodiments,layer 16 is at least 5 microns (e.g. at least 10 microns, at least 20microns) thick, and/or at most 250 microns (e.g., 200 microns, 150microns) thick. For example, layer 16 can be from five microns to 250microns (e.g., from 10 microns to 200 microns, from 20 microns to 150microns) thick. The thickness of layer 16 is determined using scanningelectron microscopy. Without wishing to be bound by theory, it isbelieved that, using the processes described herein, it is possible toobtain a layer of meltblown fibers that is thicker than is typicaland/or economically feasible for a layer of electrospun fibers, and/orthat is thinner and/or economically feasible than is typical (e.g., dueto considerations of, for example, mechanical integrity) for a layer ofmeltblown fibers.

The basis weight of layer 16 can typically be selected as desired. Insome embodiments, the basis weight of layer 16 is at least one g/m²(e.g., at least 10 g/m² , at least 25 g/m²), and/or at most 100 g/m² (atmost 90 g/m², at most 75 g/m²). For example, in certain embodiments,layer 16 has a basis weight of from one g/m² to 100 g/m² (e.g., from 10g/m² to 90 g/m², from 25 g/m² to 75 g/m²). Without wishing to be boundby theory, it is believed that, using the processes described herein, itis possible to obtain a layer of meltblown fibers that has a basisweight greater than is typical and/or economically feasible for a layerof electrospun fibers, and/or that has a basis weight that is less thanis typical (e.g., due to considerations of, for example, mechanicalintegrity and/or instantaneous lamination) for a layer of meltblownfibers.

The air permeability of layer 16 can also be varied as desired. In someembodiments, layer 16 has an air permeability of at most 500 CFM (e.g.,at most 250 CFM, at most 200 CFM), and or at least 20 CFM (e.g., atleast 50 CFM, at least 100 CFM). For example, in some embodiments, theair permability of layer 16 can be from 20 CFM to 500 CFM (e.g., from 50CFM to 250 CFM, from 100 CFM to 200 CFM). Typically, the airpermeability of layer 16 (Perm) is determined by the equation(1/Perm)=(1/Perm₁)+(1/Perm₂), where Perm is the air permeability offilter medium 10 (including layers 12, 14 and 16), Perm₁ is the airpermeability of meltblown layer 16, and Perm₂ is the air permeability ofsubstrate layer 12. For example, the air permeability of filter medium10 where meltblown layer 16 has an air permeability of 300 CFM, andsubstrate 12 has an air permeability of 70 CFM would be 56.8 CFM because1/56.8=1/300+1/70.

While shown in FIG. 1 as being continuous, in some embodiments, layer 16can be discontinuous. For example, layer 16 could be in the form amaterial with holes in it (e.g., in the form of a mesh). Additionally oralternatively, layer 16 could be in the form of patches (e.g., dots) ofmaterial.

D. Filter Medium Properties

In general, the thickness of filter medium 10 may be selected asdesired. The thickness of filter medium 10 is the distance from theouter surface of layer 12 to the outer surface of layer 16. Inembodiments in which layer 14 is an adhesive, filter medium 10 can havea thickness of the article that is at least 200 microns (e.g., at least300 microns, at least 400 microns), and/or a thickness of most 1500microns (e.g., at most 1000 microns, at most 750 microns). For example,in such embodiments, filter medium 10 has a thickness of from 200microns to 1500 microns (e.g., from 300 microns to 1000 microns, from400 microns to 750 microns). In embodiments in which layer 14 is ascrim, filter medium 10 can have a thickness of the article is at least200 microns (e.g., at least 300 microns, at least 400 microns), and/or athickness of most 2500 microns (e.g., at most 2000 microns, at most 1500microns). For example, in such embodiments, filter medium 10 has athickness of from 200 microns to 2500 microns (e.g., from 300 microns to2000 microns, from 400 microns to 1500 microns).

Generally, filter medium 10 can have any desired basis weight. Inembodiments in which layer 14 is an adhesive, filter medium 10 can havea basis weight of at most 500 g/m² (e.g. at most 400 g/m², at most 300g/m²), and or at least 30 g/m² (e.g., at least 75 g/m², at least 100g/m²). In embodiments in which layer 14 is a scrim, filter medium 10 canhave a basis weight of at most 600 g/m² (e.g. at most 500 g/m², at most400 g/m²), and or at least 50 g/m² (e.g., at least 100 g/m², at least150 g/m²).

The air permeability of filter medium 10 can usually be selected asdesired. In some embodiments, the air permeability of filter medium 10is at most 300 CFM (e.g., at most 200 CFM, at most 100 CFM), and/or atleast one CFM (e.g., at least 10 CFM, at least 25 CFM). For example, insome embodiments, filter medium 10 can have an air permeability of fromone CFM to 300 CFM (e.g., from 10 CFM to 200 CFM, from 25 CFM to 100CFM).

In some embodiments, filter medium 10 can exhibit a good ability tocapture dust. For example, in some embodiments, filter medium 10 has aninitial dust capture efficiency of at least 80% (e.g., at least about85%, at least about 90%) (see discussion below for description ofinitial dust capture efficiency test). In certain embodiments, filtermedium 10 has a periodic dust capture efficiency that is at least about90% (e.g., at least about 95%, at least about 97%) (see discussion belowfor description of periodic dust capture efficiency test). In someembodiments, filter medium 10 has an initial dust capture efficiency ofat least 80% (e.g., at least about 85%, at least about 90%) and aperiodic dust capture efficiency that is at least about 90% (e.g., atleast about 95%, at least about 97%.)

In certain embodiments, filter medium 10 can have good dust holdingproperties. For example, in certain embodiments, filter medium 10 canhave a dust holding capacity of at least 50 g/m² (e.g., at least 60g/m², at least 70 g/m²) (see discussion below for description of dustholding capacity test).

In some embodiments, filter medium 10 has both good dust capture andgood dust holding properties. As an example, in some embodiments, filtermedium 10 has an initial dust capture efficiency of at least 80% (e.g.,at least about 85%, at least about 90%) and a dust holding capacity ofat least 50 g/m² (e.g., at least 60 g/m², at least 70 g/m²). As anotherexample, in some embodiments, filter medium 10 has a periodic dustcapture efficiency of at least 90% (e.g., at least about 95%, at leastabout 97%) and a dust holding capacity of at least 50 g/m² (e.g., atleast 60 g/m², at least 70 g/m²). Without wishing to be bound by theory,it is believed that, simultaneously providing good dust capture and gooddust holding properties can result, in some embodiments at least, fromthe processes described herein, by which the article can include a layerof meltblown fibers that has a relatively small average fiber diameter(e.g., 0.8 micron or less) and is less dense and is thicker thanelectrospun coatings.

In certain embodiments, filter medium 10 has good fine particle captureproperties. As an example, in some embodiments, filter medium 10 has aNaCl particle capture test time of at least 40 minutes (e.g., at least50 minutes, at least 60 minutes, at least two hours (see discussionbelow for description of NaCl particle capture test).

In some embodiments, dust can be relatively easily removed from filtermedium 10. For example, in some embodiments, filter medium 10 has aninitial cleanability test time of at least four hours (e.g., at leastfive hours, at least six hours) (see discussion below for description ofinitial cleanability test). In certain embodiments, filter medium 10 hasan aged cleanability test time of at 70% (e.g., at least 80%, at least90%) of the initial cleanability test time (see discussion below fordescription of aged cleanability test).

In some embodiments, filter medium 10 can exhibit good NaCl particlefiltration efficiency and good NaCl particle capture. For example, insome embodiments, filter medium 10 can have a NaCl particle filtrationefficiency of at least 30% (e.g., at least 40%, at least 50%) and a NaClparticle capture test time of at least 40 minutes (e.g., at least 50minutes, at least 60 minutes) (see discussion below for description ofNaCl particle capture efficiency test and NaCl particle capture test).Without wishing to be bound by theory, it is believed that,simultaneously providing good NaCl particle filtration efficiency andgood NaCl particle capture can result, in some embodiments at least,from the processes described herein, by which the article can include alayer of meltblown fibers that has a relatively small average fiberdiameter (e.g., 0.8 micron or less) and is less dense and is thickerthan electrospun coatings.

In certain embodiments, filter medium 10 can have good liquid filtrationproperties. For example, in certain embodiments, filter medium 10 has aliquid filtration efficiency of at least 45% (e.g., at least 50%, atleast 60%) at a given particle size (see discussion below fordescription of liquid filtration efficiency test). As another example,in some embodiments, filter medium 10 has a liquid filtration retentionefficiency of at least 60% (e.g., at least 65%, at least 70%) at a givenparticle size and time (see discussion below for description of liquidfiltration efficiency test).

In certain embodiments, article 10 can have a Beta decay of at most 20%(e.g., at most 15%, at most 10%, at most 5%) at a particle size of fourmicrons. In some embodiments, article 10 has a Beta decay of at least 1%at a particle size of four microns. As used herein, the “Beta decay at aparticle size of four microns” of an article is determined according tothe ISO 16889:1999 test procedure.

In some embodiments, an article can be corrugated. Optionally, acorrugated article can also be pleated.

FIG. 4 shows an article 30 having a substrate 12, an adhesive 14 and ameltblown layer 16. Article 30 has a repeat corrugation pattern with acorrugation channel width depicted by a distance “c”, which is thedistance from one peak to its nearest neighboring peak in the repeatcorrugation pattern. In general, article 30 can have any desiredcorrugation channel width. In some embodiments, corrugation channelwidth “c” is at least 150 mils (e.g., at least 160 mils, from 167 milsto 173 mils, at least 225 mils, at least 250 mils, from 247 mils to 253mils, from 150 mils to 335 mils).

In some embodiments, article 30 has a corrugation depth on a side 12A ofsubstrate 12 that is depicted by a distance “d1”, which is the distancefrom a peak of layer 16 to a valley of layer 14 in the repeatcorrugation pattern. In some embodiments, corrugation depth “d1” is atleast 8 mils (e.g., at least 10 mils, at least 12 mils, at least 14mils, at least 16 mils), and/or at most 25 mils (e.g., at most 20 mils).

In certain embodiments, article 30 has a corrugation depth on a side 12Bof substrate 12 that is depicted by a distance “d2”, which is thedistance from a peak of side 12B of substrate 12 to a valley of side 12Bof substrate 12 in the repeat corrugation pattern. In some embodiments,corrugation depth “d2” is at least 8 mils (e.g., at least 10 mils, atleast 12 mils, at least 14 mils, at least 16 mils), and/or at most 25mils (e.g., at most 20 mils).

In some embodiments, article 30 has a retained corrugation of at least25% (e.g., at least 30%, at least 40%, at least 50%, at least 60%, atleast 70%). As referred to herein, the “retained corrugation” of article30 is determined by dividing the corrugation depth “d1” by the distancefrom a peak of side 12A substrate 12 to a valley of side 12A ofsubstrate 12 (measured before layer 14 is applied to side 12A ofsubstrate 12) in the repeat corrugation pattern, and multiplying thisvalue by 100%. Without wishing to be bound by theory, it is believedthat the retained corrugation may result from the processes disclosedherein in which layer 12 is formed on a separate web from layer 16, andthese layers are subsequently adhered to each other. In some instances,selecting appropriate pressure can enhance the retained corrugation, ifthe pressure selected is high enough to achieve desired adhesion whilebeing low enough to achieve advantageous retained corrugationproperties.

II. FILTER ASSEMBLIES AND SYSTEMS

Filter assembly 100 can be any of a variety of filter assemblies.Examples of filter assemblies include gas turbine filter assemblies,heavy duty air filter assemblies, automotive air filter assemblies, HVACair filter assemblies, HEPA filter assemblies, vacuum bag filterassemblies, fuel filter assemblies, and oil filter assemblies. Suchfilter assemblies can be incorporated into corresponding filter systems(gas turbine filter systems, heavy duty air filter systems, automotiveair filter systems, HVAC air filter systems, HEPA filter systems, vacuumbag filter systems, fuel filter systems, and oil filter systems). Vacuumfilter bag systems are commonly used in home vacuum cleaners. In suchembodiments, the filter medium can optionally be prepared by coating apaper with the meltblown material. In certain embodiments, the filtermedium can be prepared using a wet laid or dry laid product (e.g.,cellulose, polymer, glass). The filter medium can optionally be pleatedinto any of a variety of configurations (e.g., panel, cylindrical).

The orientation of filter medium 10 relative to gas flow through afilter assembly/filter system can generally be selected as desired. Insome embodiments, meltblown layer 16 is upstream of substrate 12 in thedirection of gas flow through the filter assembly/system. In certainembodiments, meltblown layer 16 is downstream of substrate 12 in thedirection of gas flow through the filter assembly/system. As an example,in some embodiments in which the gas filter system is a gas turbinefilter system or a heavy duty air filter system, meltblown layer 16 canbe upstream of substrate 12 in the direction of gas flow through thefilter assembly/system. As another example, in some embodiments in whichimproved depth filtration is desired, meltblown layer 16 can bedownstream of substrate 12 in the direction of gas flow through thefilter assembly/system.

III. METHODS OF MANUFACTURING FILTER MEDIUM

1. Adhesive

In general, in embodiments in which adhesive layer 14 is used, themanufacturing method involves applying layer 14 to substrate 12, andsubsequently applying meltblown layer 16 to adhesive 14, so that, withinfilter medium 10, substrate 12 and meltblown layer 16 are both adheredto adhesive layer 14.

In some embodiments, manufacture of filter medium 10 with adhesive layer14 involves a continuous (e.g., roll-to-roll) process. The process can,for example, involve the use of multiple roll-to-roll systems. As anexample, one roll-to-roll system can be used to form meltblown layer 16,and another roll-to-roll system can be used to adhere layer 14 tosubstrate 12. In such a system, the roll-to-roll systems can beconfigured so that, in a continuous fashion, adhesive layer 14 contactsmeltblown layer 16 and these two layers become adhered to each other.

FIG. 5 shows an embodiment of a system 200 that can be used to formfilter medium 10 having adhesive layer 14. System 200 includes a firstroll-to-roll system 210 and a second roll-to-roll system 220.

System 210 includes rollers 212 a, 212 b, 212 c and 212 d that move acontinuous belt 214 as the rollers rotate. System 212 also includes anextruder 216. As rollers 212 a-212 d are rotating, the polymer(s) (e.g.,optionally with one or more additives) are vacuum drawn into extruder216, and the polymer is heated (generally slowly) from the beginning ofthe extruder to the end, allowing the polymer(s) to flow more easily.The heated polymer(s) is(are) fed into a melt pump which controls thethroughput (lb/hr) of the polymer(s). The polymer(s) then goes through adie tip with a series of holes. It is believed that, in someembodiments, the throughput of polymer per hole can have a relatively astrong affect on fiber diameter. Heated, high velocity air impinges thepolymer on either side of the die tip as the polymer comes out of thedie tip. It is believed that this air can attenuate the fiber to thefinal fiber size. It is believed that, in some embodiments, as theprocess air throughput increases, the fiber diameter can decrease,and/or that, as the process air temperature increases, the fiberdiameter can decrease. In the area where fiber attenuation occurs,quench air is present, which forms an area where fiber formation occursat the same temperature year round. The distance from the die tip to thecollector allows us to control the density of the material (e.g., as thecollector distance is increased, the fiber velocity is decreased and thefiber temperature is reduced so packing of the fibers is less dense,resulting in a more lofty web). As the distance is increased, thevelocity of the fiber is generally decreased, making a loftier filtermedia. The collector suction is also controlled, which also impacts theloft of the material. It is believed that, in some embodiments, as thebelt speed is increased, the web basis weight of the filter medium candecrease, and/or that, as the polymer throughput increases, the basisweight of the filter medium can increase.

The size of the holes and number of holes per inch for the die cangenerally be selected as desired. In some embodiments, the die can have35 holes per inch with 0.0125″ holes. In certain embodiments, the diecan have 70 holes per inch with 0.007″ holes. Other dies can optionallybe used.

System 220 includes rollers 222 a, 222 b, 222 c and 222 d that movesubstrate 12 as the rollers rotate. Between rollers 222 a and 222 b,system 220 includes a station 226 that applies an adhesive to substrate12. In a region adjacent rollers 222 b and 212 a, the adhesive contactsmeltblown layer 16, and meltblown layer 16 is removed from belt 214 andadhered to the adhesive. The substrate/adhesive/meltblown layercomposite then passes through a charging unit 228. Charging unit 228 isused to charge the composite (in general, particularly the meltblownlayer). It is believed that this can result in a filter medium havingenhanced fine particle capture properties. It is believed that thecharging process can embed charges in the meltblown material.

Station 226 can generally be selected as desired. In some embodiments(e.g., when it is desirable to have a relatively high coverage ofadhesive), station 226 can be a metered adhesive system. The meteredadhesive system can be configured to apply a relatively highly dispersedand uniform amount of adhesive. In certain embodiments, station 226 is aNordson Precision Metered Gear Adhesion applicator system with Signaturenozzles, which can have 12 nozzles per inch that provide dispersedadhesion lanes with a two millimeter gap between center points of thelanes and with each nozzle having a 0.06 inch diameter orifice.

In general, the temperature is selected to properly soften (e.g., melt)the material that is to be formed into layer 16. As an example, in someembodiments, the material is heated to a temperature of at least 350° F.(e.g., at least 375° F., at least 400° F.), and or at most 600° F.(e.g., 550° F., at most 500° F.). For example, the material can beheated to a temperature of from 350° F. to 600° F. (e.g., from 375° F.to 550° F., from 400° F. to 500° F.).

In general, the process air is the heated air on either side of the dietip where the fibers are formed. This heated air (typically the sametemperature as the die tip) impinges the fibers and helps attenuate thefibers to the final fiber size. It is believed that, in someembodiments, as the air volume increases, the fiber diameter candecrease. The process air volume can be selected as appropriate. In someembodiments, the process air volume is at least 2500 pounds/hour-meter(e.g., at least 2750 pounds/hour-meter, at least 3000pounds/hour-meter), and/or at most 4000 pounds/hour-meter (e.g., at most3750 pounds/hour-meter, at most 3500 pounds/hour-meter). For example,the process air volume can be from 2500 pounds/hour-meter to 4000pounds/hour-meter (e.g., from 2750 pounds/hour-meter to 3750pounds/hour-meter, from 3000 pounds/hour-meter to 3500pounds/hour-meter).

The vacuum created by vacuum 218 can be selected as appropriate. In someembodiments, the vacuum is at least 10 inches of water (e.g., at least12 inches of water, at least 14 inches of water), and/or at most 26inches of water (e.g., at most 23 inches of water, at most 20 inches ofwater). For example, the vacuum can be from 10 inches of water to 26inches of water (e.g., from 12 inches of water to 23 inches of water,from 14 inches of water to 20 inches of water).

Belt 214 generally can be made of any material that allows the formationof layer 16 on belt 214, and also allows the removal of layer 16 frombelt 214 when layer 16 contacts adhesive layer 14. Examples of materialsfrom which belt 214 can be made include polymers (e.g., polyesters,polyamides), metals and/or alloys (e.g., stainless steel, aluminum).

The speed at which belt 214 moves can be selected as desired to formlayer 16. In some embodiments, the belt 214 moves at a speed of least 10ft/min (e.g., at least 20 ft/min, at least 30 ft/min), and/or at most300 ft/min (e.g., at most 200 ft/min, at most 100 ft/min). For example,belt 214 can move at a speed of from 10 ft/min to 300 ft/min (e.g., from20 ft/min to 200 ft/min, from 30 ft/min to 100 ft/min).

In general, when applied to substrate 12, the temperature of theadhesive can be selected so that it has an appropriate level of tackwhen it comes into contact with layer 16. In embodiments in which theadhesive is a hot melt adhesive, this can involve heating the adhesiveprior to its application to substrate 12. For example, prior to beingapplied to substrate 12, the adhesive can be heated to a temperature ofat least 350° F. (e.g., at least 370° F., at least 380° F.), and or atmost 450° F. (e.g., 430° F., at most 420° F.). For example, the materialcan be heated to a temperature of from 350° F. to 450° F. (e.g., from370° F. to 430° F., from 380° F. to 420° F.).

Substrate 12 is typically fed through the adhesive station by thepulling force generated via a nip formed at rollers 212 a and 222 b. Bycontacting substrate 12 adjacent roller 222 b (e.g., a rubber roller,such as a 70 Shore A EPDM rubber roller) with meltblown material 16adjacent roller 212 a (e.g., a stainless steel roller, such as astainless steel roller that is crowned by 0.025 inch), the speed of belt214 and substrate 12 are synchronized (e.g., so that substrate 12 movesat approximately the same speed as belt 214). The pressure betweenrollers 212 a and 222 b is generally selected as desired for theintended use of article 10. For example, in embodiments in which article10 is corrugated, the pressure between rollers 212 a and 222 b istypically selected to achieve good corrugation depth and conformity forarticle 10. In some embodiments, the pressure between rollers 212 a and222 b is from 20 pounds per linear inch to 40 pounds per linear inch(e.g., from 25 pounds per linear inch to 35 pounds per linear inch, from28 pounds per linear inch to 32 pounds per linear inch, from 29 poundsper linear inch to 31 pounds per linear inch, 30 pounds per linearinch).

In general, any of a variety of techniques can be used to charge thesubstrate/adhesive/meltblown layer composite to form an electret web.Examples include AC and/or DC corona discharge and friction-basedcharging techniques. In some embodiments, the composite is subjected toa discharge of at least 1 kV/cm (e.g., at least 5 kV/cm, at least 10kV/cm), and/or at most 30 kV/cm (e.g., at most 25 kV/cm, at most 20kV/cm). For example, in certain embodiments, the composite can besubjected to a discharge of from 1 kV/cm to 30 kV/cm (e.g., from 5 kV/cmto 25 kV/cm, from 10 kV/cm to 20 kV/cm). Exemplary processes aredisclosed, for example, in U.S. Pat. No. 5,401,446, which, to the extentit is not inconsistent with the present disclosure, is incorporatedherein by reference.

In general, any belt configuration can be used. For example, in someembodiments, the belt has an open structure, such as a mesh structure.Without wishing to be bound by theory, it is believed that such an openstructure results in the meltblown material having a complementarystructure to that of the belt because the meltblown material is underthe force of the blown air. FIG. 6 shows a cross section of themeltblown material 60 having a series of crests 64 and valleys 62resulting from the complementary shape of the belt. Without wishing tobe bound by theory, it is believed that this structure may be present inthe meltblown material in the filter medium, and that, during collectionof dust or other particles, the dust may build up in the valleys,allowing for good dust removal during pulsing. In some embodiments, thedistance d between adjacent valleys 62 is at least 400 microns (e.g., atleast 500 microns, at least 700 microns), and/or at most 2000 microns(e.g., at most 1500 microns, at most 1200 microns). In some embodiments,the distance d between adjacent valleys 62 is from 400 microns to 2000microns (e.g., from 500 microns to 1500 microns, from 700 microns to1200 microns). In some embodiments, the distance h from a crest 64 to avalley 62 is at least 50 microns (e.g., at least 100 microns, at least300 microns), and/or at most 2000 microns (e.g., at most 1500 microns,at most 1000 microns). In some embodiments, the distance h from a crest64 to a valley 62 is from 50 microns to 2000 microns (e.g., from 200microns to 1500 microns, from 300 microns to 1000 microns).

2. Scrim

In general, in embodiments in which scrim layer 14 is used, themanufacturing method involves applying meltblown layer 16 to scrim 14,subsequently applying substrate 12 to scrim 14, and then bonding thethree layers together.

In some embodiments, manufacture of filter medium 10 with scrim layer 14involves a continuous (e.g., roll-to-roll) process. The process can, forexample, involve the use of multiple roll-to-roll systems. As anexample, one roll-to-roll system can be used to form meltblown layer 16on scrim 14, and another roll-to-roll system can be used to carrysubstrate 12. In such a system, the roll-to-roll systems can beconfigured so that, in a continuous fashion, the meltblown layer/scrimcomposite contacts substrate 12 to form a three layer composite, and thethree layers are subsequently bonded together.

FIG. 7 shows an embodiment of a system 300 that can be used to formmeltblown layer 16 on scrim 14. System 300 includes rollers 302 a, 302b, 302 c and 302 d that move a continuous belt 304 as the rollersrotate. Scrim 14 is applied to belt 304. System 302 also includes anextruder 306. As rollers 302 a-302 d are rotating, extruder 306 isheated, and the material from which layer 16 is to be formed (e.g., apolymer in pellet form) is introduced into heated extruder 306. Thematerial is softened (e.g., melted) and forced through a die 307 in theform of filaments. The filaments are moved toward scrim 14 under theinfluence of a vacuum 308 on the opposite side of belt 304 relative todie 307. The effect of the vacuum is to stretch the filaments and forcethem against the surface of scrim 14 to provide meltblown layer 16disposed on scrim 14.

The process conditions used for the process described in FIG. 7 cangenerally be selected as desired to form layer 16. In general, thetemperature is selected to properly soften (e.g., melt) the materialthat is to be formed into layer 16. As an example, in some embodiments,the material is heated to a temperature of at least 350° F. (e.g., atleast 375° F., at least 400° F.), and or at most 600° F. (e.g., 550° F.,at most 500° F.). For example, the material can be heated to atemperature of from 350° F. to 600° F. (e.g., from 375° F. to 550° F.,from 400° F. to 500° F.).

In general, the process air is the heated air on either side of the dietip where the fibers are formed. This heated air (typically the sametemperature as the die tip) impinges the fibers and helps attenuate thefibers to the final fiber size. It is believed that, in someembodiments, increasing the air volume can result in a reduced fiberdiameter. The process air volume can be selected as appropriate. In someembodiments, the process air volume is at least 2500 pounds/hour-meter(e.g., at least 2750 pounds/hour-meter, at least 3000pounds/hour-meter), and/or at most 4000 pounds/hour-meter (e.g., at most3750 pounds/hour-meter, at most 3500 pounds/hour-meter). For example,the process air volume can be from 2500 pounds/hour-meter to 4000pounds/hour-meter (e.g., from 2750 pounds/hour-meter to 3750pounds/hour-meter, from 3000 pounds/hour-meter to 3500pounds/hour-meter).

The vacuum created by vacuum 308 can be selected as appropriate. In someembodiments, the vacuum is at least 10 inches of water (e.g., at least12 inches of water, at least 14 inches of water), and/or at most 26inches of water (e.g., at most 23 inches of water, at most 20 inches ofwater). For example, the vacuum can be from 10 inches of water to 26inches of water (e.g., from 12 inches of water to 23 inches of water,from 14 inches of water to 20 inches of water).

The speed at which belt 304 moves can be selected as desired to formlayer 16. In some embodiments, the belt 304 moves at a speed of least 10ft/min (e.g., at least 20 ft/min, at least 30 ft/min), and/or at most300 ft/min (e.g., at most 200 ft/min, at most 100 ft/min). For example,belt 304 can move at a speed of from 10 ft/min to 300 ft/min (e.g., from20 ft/min to 200 ft/min, from 30 ft/min to 100 ft/min).

The scrim/meltblown layer composite is removed from belt 304, andsubstrate 12 is disposed on scrim 14. Typically, this involves bringingscrim 14 onto a belt (e.g., belt 214) and then blowing the meltblownfibers directly onto scrim 14. Scrim 14 can have adhesive applied beforethe meltblown is blown on or the force and the heat of the meltblownfibers can be used to adhere the two layers together. The relevantprocess conditions are generally the same as above. The three layers arethen bonded together. During this process, the three layers canoptionally be laminated together. In some embodiments, the layers areultrasonically bonded together (e.g., ultrasonically point bondedtogether). In some embodiments, meltblown layer 16, scrim 14 andsubstrate 12 can be joined by applying ultrasonic energy between analuminum vibrating horn (½″ contact width, from Branson Ultrasonics,Danbury, Conn.) and an engraved contact roll. In certain embodiment, themethod involves using a horn pulsing at 20 kHZ applying 20 to 30 psi ofcontact pressure at an amplitude of 20 to 35 microns at a feed rate of25 to 45 ft/min bonds the composite together at points comprising ofless than 10% (e.g., less than 8%, less than 5%, less than 3%) of thetotal area as determined by the engraving on the contact roll.

The following examples are exemplary and not intended as limiting.

IV. EXAMPLES

A. Test Protocols

1. NaCl Particle Filtration Efficiency Test

A 100 cm² surface area of the filter medium was tested with NaCl (sodiumchloride) particles having a 0.26 micron mass mean diameter with ageometric standard deviation less than 1.83, a concentration of 15 to 20mg/cm³, and a face velocity of 5.3 cm/s by a TSI8130 CertiTest™automated filter testing unit from TSI, Inc. equipped with a sodiumchloride generator. The instrument measured a pressure drop across thefilter media and the resultant penetration value on an instantaneousbasis at a flow rate less than or equal to 115 liters per minute (lpm).Instantaneous readings were defined as 1 pressure drop/penetrationmeasurement. This test is described in ASTM D2 986-91. The NaCl particlefiltration efficiency is [100−(C/C₀)]*100%, where C was the particleconcentration after passage through the filter and C₀ was the particleconcentration before passage through the filter.

2. Initial Dust Capture Efficiency, Periodic Dust Capture Efficiency andDust Holding Capacity

A 100 cm² surface area of the filter medium was challenged with a finedust (0.1-80 μM) at a concentration of 200 mg/cm³ with a face velocityof 20 cm/s for one minute. The dust capture efficiency was measuredusing a Palas MFP2000 fractional efficiency photodetector. The dustcapture efficiency was [(100−[C/C0])*100%], where C was the dustparticle concentration after passage through the filter and C0 was theparticle concentration before passage through the filter. The dustcapture efficiency was measured after one minute and is referred toherein as the initial dust capture efficiency. The dust captureefficiency was also measured periodically after one minute and isreferred to herein as the periodic dust capture efficiency. The dustholding capacity is measured when the pressure reaches 1800 Pa, and isthe difference in the weight of the filter medium before the exposure tothe fine dust and the weight of the filter medium after the exposure tothe fine dust.

3. Initial Cleanability Test and Aged Cleanability Test

An AC fine dust at 16 g/hr was sent through the filter medium at a facevelocity of 5 cm/s, and then subject to 150 millisecond pulse at 4 barto remove particles from the medium when the medium reaches a pressureof 10 mBar. This process (exposure to the AC fine dust under the statedconditions until reaching a pressure of 10 mBar) is repeated a total of30 times, and the initial cleanability time is the amount of time ittakes to complete the 30 cycles. The medium is then aged by continuousexposure to the AC dust (12 g/hr) for 10,000 Cycles and pulsed 14 timesper minute. After this ageing process, the filter medium is againexposed to the AC fine dust under the conditions noted above 30 times,and the aged cleanability time is the amount of time it takes tocomplete these 30 cycles. This test is performed on a Palas MMTC-2000Cleanability test stand by VDI-3926 type 2 Procedure with a test area of177 cm².

4. NaCl Particle Capture Test

A surface area of 100 cm² was exposed to an aerosol of 0.4 to 0.5 μMNaCl particles at 2% concentration at a face velocity of 8.3 cm/s with atotal flow volume of 45 liters/min. The NaCl particle capture test timeis the amount of time it takes to reach a pressure of 1800 Pa.

5. Liquid Filtration Efficiency Test and Liquid Filtration RetentionEfficiency

Using a FTI Multipass Filter Test Stand (Fluid Technologies Inc.,Stillwater, Okla.), an A2 fine dust is fed at a rate of 0.3 liters perminute into Mobil MIL-H-5606 fuel for a total flow rate of 1.7 litersper minute to contact the filter medium per ISO 16889 until a terminalpressure of 174 KPa above the baseline filter pressure drop is obtained.Particle counts (particles per milliliter) are taken at the particlesize selected (in this case 4, 5, 7, 10, 15, 20, 25 and 30 microns)upstream and downstream of the media are taken at ten points equallydivided over the time of the test. The average of upstream anddownstream particle counts are taken at each selected particle size.From the average particle count upstream (injected −C₀) and the averageparticle count downstream (passed thru-C) the liquid filtrationefficiency test value for each particle size selected is determined bythe relationship [(100−[C/C₀])*100%]. The liquid filtration retentionefficiency as a function of time and particle size can also be measuredby comparing the upstream and downstream particle counts (anddetermining efficiency [(100−[C/C0])*100%]) at the sequential ten pointsin the test.

B. Examples

1. Sample A

Sample A was prepared by forming a 7 g/m² (gsm) meltblown web from 0.8micron polypropylene fibers (Exxon PP3546 G, ExxonMobil ChemicalCompany, Houston, Tex.) produced at a polymer heated to 475° F. at rateof 36 lbs of polymer/hr from a 35 holes per inch die blown by processair heated to 475° F. at a flow rate of 3900 bs/hr while quenching with55° F. air of 390 lbs/hr. The meltblown material was collected andinstantaneously bonded onto a 10 gsm spunbond polypropylene nonwovenscrim (Celestra from Fiberweb Corporation, Nashville, Tenn.) moving on acollector belt moving at 55 ft/min with a vacuum pressure ofapproximately 18 inches of water through a 7 inch wide slot. Themeltblown was adhered to the spunbond giving a composite structure withcaliper of 0.0055″, a basis weight of 18 gsm, air permeability of 91 cfmat 0.5″ water column. The resulting filter media had a pressure drop of1.5 mm H2O @ 10.5 FPM face velocity, as determined with a TSI 8130filtration tester. The NaCl particle filtration efficiency was 82.2%.

The meltblown nanofiber/scrim combination was adhered to a support layerformed from a cellulose fiber containing 17% vinyl acetate resin and 83%cellulosic fiber wet laid nonwoven with a basis weight of 139 gsm and anair permeability of 80 cfm at 0.5″ water. The meltblownnanofiber/spunbond was ultrasonically point bonded (3% bond area) to acellulose support with the cellulose support positioned on thedownstream side of the meltblown nanofiber scrim with the scrimpositioned upstream of the meltblown nanofiber.

The filter media had a basis weight of 156 gsm, a caliper of 0.030″ andan air permeability of 38 cfm at 0.5″ water column. The NaCl particlefiltration efficiency was 87.5%. This is an improvement over theuncoated cellulose substrate (approximately 11%). The spunbond scrim hasessentially no ability to capture fine particles.

2. Sample B

Sample B was prepared by forming a 1 gsm meltblown web from 0.25 micronpolypropylene fibers (Exxon PP3546 G, ExxonMobil Chemical Company,Houston, Tex.) produced at a polymer heated to 425° F. at rate of 2 lbsof polymer/hr from a 70 holes per inch die blown by process air heatedto 450° F. at a flow rate of 3250 lbs/hr while quenching with 55° F. airat 350 lbs/hr. The meltblown material was collected and instantaneouslybonded onto a 10 gsm spunbond polypropylene scrim (Celestra fromFiberweb Corporation, Nashville, Tenn.) moving on a collector beltmoving at 30 ft/min with a vacuum pressure of approximately 20 inches ofwater through a 7 inch wide slot.

The meltblown was adhered to the spunbond giving a composite structurewith caliper of 0.0034″, a basis weight of 11 gsm, air permeability of328 cfm at 0.5″ water column. The resulting filter media had a pressuredrop of 0.4 mmH2O @ 10.5 FPM face velocity, as determined with a TSI8130 filtration tester. The NaCl particle filtration efficiency was 47%.

The meltblown nanofiber/scrim combination was adhered to a support layerformed from a cellulose fiber containing 17% vinyl acetate resin and 83%cellulosic fiber wet laid nonwoven with a basis weight of 139 gsm and anair permeability of 80 cfm at 0.5″ water. The meltblownnanofiber/spunbond was ultrasonically bonded to a cellulose support withthe cellulose support positioned on the downstream side of the meltblownnano fiber scrim with the scrim positioned upstream of the meltblownnanofiber.

The filter media had a basis weight of 156 gsm, a caliper of 0.032″ andan air permeability of 53 cfm at 0.5″ water column. The NaCl particlefiltration efficiency was 53%. This is an improvement over the uncoatedcellulose substrate (approximately 11%). The spunbond scrim hasessentially no ability to capture fine particles.

3. Sample C

Sample C was prepared by forming a 2 gsm meltblown web from 0.32 micronpolypropylene fibers (Exxon PP3546 G, ExxonMobil Chemical Company,Houston, Tex.) produced at a polymer heated to 425° F. at rate of 12 lbsof polymer/hr from a 70 holes per inch die blown by process air heatedto 450° F. at a flow rate of 3250 lbs/hr while quenching with 55° F. airat 350 lbs/hr. The meltblown material was collected and instantaneouslybonded onto a 10 gsm spunbond polypropylene scrim (Celestra fromFiberweb Corporation, Nashville, Tenn.) moving on a collector beltmoving at 75 ft/min with a vacuum pressure of approximately 20 inches ofwater through a 7 inch wide slot. The meltblown was adhered to thespunbond giving a composite structure with caliper of 0.0052″, a basisweight of 12 gsm, air permeability of 335 cfm at 0.5″ water column. Theresulting filter media had a pressure drop of 0.3 mmH2O @ 10.5 FPM facevelocity, as determined with a TSI 8130 filtration tester. The NaClparticle filtration efficiency was 36%.

The meltblown nanofiber/scrim combination was adhered to a support layerformed from a cellulose fiber containing 17% vinyl acetate resin and 83%cellulosic fiber wet laid nonwoven with a basis weight of 139 gsm and anair permeability of 80 cfm at 0.5″ water.

The meltblown nanofiber/spunbond was ultrasonically bonded to acellulose support with the cellulose support positioned on thedownstream side of the meltblown nanofiber scrim with the scrimpositioned upstream of the meltblown nanofiber.

The filter media had a basis weight of 156 gsm, a caliper of 0.031″ andan air permeability of 56 cfm at 0.5″ water column. The NaCl particlefiltration efficiency was 49%. This is an improvement over the uncoatedcellulose substrate (approximately 11%).

4. Sample D

Sample D was prepared by forming a 5 gsm meltblown web from 0.7 micronpolypropylene fibers (Exxon PP3546 G, ExxonMobil Chemical Company,Houston, Tex.) produced from a polymer heated to 425° F. at rate of 20lbs of polymer/hr from a 70 holes per inch die blown by process airheated to 450° F. at a flow rate of 3250 lbs/hr while quenching with 55°F. air at 490 lbs/hr. The meltblown material was collected andinstantaneously bonded onto a 10 gsm spunbond polypropylene nonwovenscrim (Celestra from Fiberweb Corporation, Nashville, Tenn.) moving on acollector belt moving at 50 ft/min with a vacuum pressure ofapproximately 20 inches of water through a 7 inch wide slot. Themeltblown was adhered to the spunbond giving a composite structure withcaliper of 0.004″, a basis weight of 15 gsm, air permeability of 111 cfmat 0.5″ water column.

The meltblown nanofiber/scrim combination was adhered to a support layerformed from a cellulose fiber containing 17% vinyl acetate resin, 15%polyester fibers and 68% cellulosic fiber wet laid nonwoven with a basisweight of 122 gsm and an air permeability of 94 cfm at 0.5″ water.

The meltblown nanofiber/spunbond was adhered to the cellulose support byapplication of a hot melt glue (Bostik HM 4379 Amorphous Polyolefin(APO)) spray at an areal weight of 4 g/m2 to the cellulose support andthen immediately bonding the glue applied layer to themeltblown/nanofiber cellulose by contact pressure between two rubberrolls. The article was made into a filter element having the scrim layerfacing the inlet and the meltblown nanofiber in the middle and thecellulose support facing the downstream side.

The filter media had a basis weight of 136 gsm, a caliper of 0.031″ andan air permeability of 51 cfm at 0.5″ water column. The NaCl particlefiltration efficiency was 68%. This is an improvement over the uncoatedcellulose substrate (approximately 11%).

5. Sample E

Sample E was prepared by forming a 5 gsm meltblown web from 0.5 micronpolypropylene fibers (Exxon PP3546 G, ExxonMobil Chemical Company,Houston, Tex.) produced from a polymer heated to 425° F. at rate of 20lbs of polymer/hr from a 70 holes per inch die blown by process airheated to 450° F. at a flow rate of 3250 lbs/hr while quenching with 55°F. air at 490 lbs/hr. The meltblown material was collected on the barecollector belt moving at 45 ft/min with a vacuum pressure ofapproximately 20 inches of water through a 7 inch wide slot. The freestanding nanofiber meltblown had a caliper of less than 0.001″, a basisweight of 5 gsm, air permeability of 100 cfm at 0.5″ water column.

The meltblown nanofiber was adhered to a support layer formed from acellulose fiber containing 17% vinyl acetate resin 15% polyester fibersand 68% cellulosic fiber wet laid nonwoven with a basis weight of 122gsm and an air permeability of 94 cfm at 0.5″ water.

The meltblown nanofiber/spunbond was adhered to the cellulose support byapplication of a hot melt glue (Bostik HM 4379 APO) spray at an arealweight of 4 g/m2 to the cellulose support and then immediately bondingthe glue applied layer to the meltblown/nano fiber cellulose by contactpressure between a belt used to collect the meltblown fibers and arubber roller. The article was made into a filter element having themeltblown nano fiber facing the inlet and the cellulose support facingthe downstream side.

The filter media had a basis weight of 133 gsm, a caliper of 0.029″ andan air permeability of 50 cfm at 0.5″ water column. The NaCl particlefiltration efficiency was 63%. This is an improvement over the uncoatedcellulose substrate (approximately 11%). The mean peel strength ofnanofiber layer from the base substrate was 0.5 ounce per inch width.

6. Sample F

Sample F was prepared by forming a 5 gsm meltblown web from 0.7 micronpolypropylene fibers (Exxon PP3546 G, ExxonMobil Chemical Company,Houston, Tex.) produced from a polymer heated to 425 F at rate of 20 lbsof polymer/hr from a 70 holes per inch die blown by process air heatedto 435 F at a flow rate of 3900 lbs/hr while quenching with 55° F. airat 520 lbs/hr. The meltblown material was collected on the barecollector belt moving at 60 ft/min with a vacuum pressure ofapproximately 20 inches of water through a 7 inch wide slot. The freestanding nanofiber meltblown had a caliper of less than 0.001″, a basisweight of 5 gsm, air permeability of 172 cfm at 0.5″ water column.

The meltblown nanofiber was adhered to a support layer formed from acellulose fiber containing 17% vinyl acetate resin and 83% cellulosicfiber wet laid nonwoven with a basis weight of 125 gsm and an airpermeability of 32 cfm at 0.5″ water.

The meltblown nanofiber was adhered to the cellulose support byapplication of a hot melt glue (Bostik HM 4379 APO) spray at an arealweight of 4 g/m2 to the cellulose support and then immediately bondingthe glue applied layer to the meltblown/nanofiber cellulose by contactpressure between a belt used to collect the meltblown fibers and arubber roller. The article was made into a filter element having themeltblown nanofiber facing the inlet and the cellulose support facingthe downstream side.

The filter media had a basis weight of 134 gsm, a caliper of 0.027″ andan air permeability of 27 cfm at 0.5″ water column. The NaCl particlefiltration efficiency was 50%. This is an improvement over the uncoatedcellulose substrate (approximately 20%).

7. Sample G

Sample G was prepared by forming a 3 gsm meltblown web from 0.7 micronpolypropylene fibers (Exxon PP3546 G, ExxonMobil Chemical Company,Houston, Tex.) produced from a polymer heated to 425° F. at rate of 20lbs of polymer/hr from a 70 holes per inch die blown by process airheated to 435° F. at a flow rate of 4250 lbs/hr while quenching with 55°F. air at 520 lbs/hr. The meltblown material was collected on the barecollector belt moving at 100 ft/min with a vacuum pressure ofapproximately 17 inches of water through a 7 inch wide slot. The freestanding nanofiber meltblown had a caliper of less than 0.001″, a basisweight of 3 gsm, air permeability of 300 cfm at 0.5″ water column.

The meltblown nanofiber was adhered to a support layer formed fromcellulose fiber containing 17% vinyl acetate resin and 83% cellulosicfiber wet laid nonwoven with a basis weight of 125 gsm and an airpermeability of 32 cfm at 0.5″ water.

The meltblown nanofiber/spunbond was adhered to the cellulose support byapplication of a hot melt glue (Bostik HM 4379 APO) spray at an arealweight of 4 g/m2 to the cellulose support and then immediately bondingthe glue applied layer to the meltblown/nano fiber cellulose by contactpressure between a belt used to collect the meltblown fibers and arubber roller. The resulting article was made into a filter having themeltblown nano fiber facing the inlet and the cellulose support facingthe downstream side.

The filter media had a basis weight of 129 gsm, a caliper of 0.025″ andan air permeability of 29 cfm at 0.5″ water column. The NaCl particlefiltration efficiency was 37%. This is an improvement over the uncoatedcellulose substrate (approximately 20%).

8. Sample H

Sample H was prepared by forming a 3 gsm meltblown web from 0.7 micronpolypropylene fibers (Exxon PP3546 G, ExxonMobil Chemical Company,Houston, Tex.) produced from a polymer heated to 425° F. at rate of 20lbs of polymer/hr from a 70 holes per inch die blown by process airheated to 440° F. at a flow rate of 4360 lbs/hr while quenching with 55°F. air at 490 lbs/hr. The meltblown material was collected on the barecollector belt moving at 100 ft/min with a vacuum pressure ofapproximately 17 inches of water through a 7 inch wide slot. The freestanding nanofiber meltblown had a caliper of less than 0.001″, a basisweight of 3 gsm, air permeability of 307 cfm at 0.5″ water column.

The meltblown nanofiber was adhered to a support layer formed fromcellulose fiber containing 17% vinyl acetate resin and 83% cellulosicfiber wet laid nonwoven with a basis weight of 139 gsm and an airpermeability of 89 cfm at 0.5″ water.

The meltblown nanofiber was adhered to the cellulose support byapplication of a hot melt glue (Bostik HM 4379 APO) spray at an arealweight of 2 g/m2 to the cellulose support and then immediately bondingthe glue applied layer to the meltblown/nanofiber cellulose by contactpressure between a belt used to collect the meltblown fibers and arubber roller. The resulting article was made into a filter having thecellulose support facing the inlet and the meltblown nano fiber layerfacing the downstream side.

The filter media had a basis weight of 143 gsm, a caliper of 0.029″ andan air permeability of 69 cfm at 0.5″ water column. The NaCl particlefiltration efficiency was 30%. This is an improvement over the uncoatedstiff backer support substrate (approximately 9%).

9. Sample I

Sample I was prepared by forming a 11 gsm meltblown web from 0.7 micronpolypropylene fibers (Exxon PP3546 G, ExxonMobil Chemical Company,Houston, Tex.) produced from a polymer heated to 425° F. at rate of 30lbs of polymer/hr from a 70 holes per inch die blown by process airheated to 440° F. at a flow rate of 4360 lbs/hr while quenching with 55°F. air at 490 lbs/hr. The meltblown material was collected on the barecollector belt moving at 37 ft/min with a vacuum pressure ofapproximately 20 inches of water through a 7 inch wide slot. The freestanding nanofiber meltblown had a caliper of less than 0.003″, a basisweight of 11 gsm, air permeability of 66 cfm at 0.5″ water column.

The meltblown nanofiber was adhered to a stiff backer carded non-wovensupport layer formed from polymeric fibers with a basis weight of 107gsm and an air permeability of 435 cfm at 0.5″ water.

The meltblown nanofiber was adhered to the stiff backer carded non-wovensupport by application of a hot melt glue (Bostik HM 4379 APO) spray atan areal weight of 4 g/m2 to the cellulose support and then immediatelybonding the glue applied layer to the meltblown/nano fiber by contactpressure between a belt used to collect the meltblown fibers and arubber roller. The resulting article was made into a filter having thestiff backer carded nonwoven support facing the inlet and the meltblownnanofiber layer facing the downstream side.

The filter media had a basis weight of 113 gsm, a caliper of 0.024″ andan air permeability of 57 cfm at 0.5″ water column. The NaCl particlefiltration efficiency was 88%. This is an improvement over the uncoatedcellulose substrate (approximately 20%).

10. Sample J

Sample J was prepared by forming a 24 gsm meltblown web from 0.5 micronPBT fibers (Ticona Celanex 2008) produced from a polymer heated to 530°F. at rate of 20 lbs of polymer/hr from a 35 holes per inch die blown byprocess air heated to 550° F. at a flow rate of 2600 lbs/hr. Themeltblown material was collected on the bare collector belt moving at 30ft/min with a vacuum pressure of approximately 20 inches of waterthrough a 7 inch wide slot. The free standing nanofiber meltblown had acaliper of 0.008″, a basis weight of 24 gsm, air permeability of 79 cfmat 0.5″ water column.

The meltblown nanofiber was adhered to a support layer formed from acellulose fiber containing 17% vinyl acetate resin 85% cellulosic fiberwet laid nonwoven with a basis weight of 165 gsm and an air permeabilityof 12 cfm at 0.5″ water.

The 4 layers of the meltblown nanofiber/spunbond was ultrasonicallybonded to a cellulose support with the cellulose support positioned onthe upstream side and the meltblown nanofiber scrim on the downstreamside.

The filter media had a basis weight of 287 gsm, a caliper of 0.045″ andan air permeability of 7 cfm at 0.5″ water column.

11. Sample K

Sample K was prepared by forming a 10 gsm meltblown web from 2 micronpolypropylene fibers (Exxon PP3546 G, ExxonMobil Chemical Company,Houston, Tex.) produced at a polymer heated to 500° F. at rate of 240lbs of polymer/hr from a 35 holes per inch die blown by process airheated to 500° F. at a flow rate of 3250 lbs/hr while quenching with 55°F. air at 350 lbs/hr. The meltblown material was collected andinstantaneously bonded onto a 10 gsm spunbond polypropylene scrim(Celestra from Fiberweb Corporation, Nashville, Tenn.) moving on acollector belt moving at 250 ft/min with a vacuum pressure ofapproximately 20 inches of water through a 7 inch wide slot. To thismeltblown/scrim composite, a nanofiber layer was added by forming a 4gsm meltblown web from 0.5 micron polypropylene fibers (Exxon PP3546 G,ExxonMobil Chemical Company, Houston, Tex.) produced at a polymer heatedto 425° F. at rate of 20 lbs of polymer/hr from a 35 holes per inch dieblown by process air heated to 450° F. at a flow rate of 3250 lbs/hrwhile quenching with 55° F. air at 350 lbs/hr.

The resulting three layer composite had a nanofiber meltblown on the topsurface, a conventional meltblown structure underneath and a scrim onthe bottom surface. The resulting composite had a basis weight of 25gsm, a caliper of 0.012″ and an air permeability of 84 cfm at 0.5″ watercolumn. The NaCl particle filtration efficiency was 88%.

12. Sample L

Sample L was prepared by forming a 5 gsm meltblown web from 0.4 micronpolypropylene fibers (Exxon PP3546 G, ExxonMobil Chemical Company,Houston, Tex.) produced from a polymer heated to 450° F. at rate of 20lbs of polymer/hr from a 35 holes per inch die blown by process airheated to 450° F. at a flow rate of 4360 lbs/hr while quenching with 55°F. air at 490 lbs/hr. The meltblown material was collected on the barecollector belt moving at 45 ft/min with a vacuum pressure ofapproximately 20 inches of water through a 7 inch wide slot. The freestanding nanofiber meltblown had a caliper of less than 0.001″, a basisweight of 5 gsm, air permeability of 150 cfm at 0.5″ water column.

The meltblown nanofiber was adhered to a corrugated support layer formedfrom a cellulose fiber containing 20% vinyl acetate resin 80% cellulosicfiber wet laid nonwoven with a basis weight of 114 gsm and an airpermeability of 16 cfm at 0.5″ water. The corrugated support layer had acorrugation channel width of 0.170″. The corrugation depth of thesupport layer was 0.022″ on the felt side to be coated, the opposite(Wire) side had a corrugation depth of 0.022″ as measured with the IASLaser Corrugation Gauge.

The meltblown nanofiber was adhered to the cellulose support byapplication of a hot melt glue (Bostik M2751 adhesive) heated to 400° F.and sprayed at 410° F. at an areal weight of 6 g/m² to the cellulosesupport and then immediately bonding the glue applied layer to themeltblown/nanofiber cellulose by contact pressure between a stainlesssteel belt used to collect the meltblown fibers and a rubber roller at anip pressure of 30 pounds per linear inch (PLI). The resulting articlewas made into a filter having the meltblown nanofiber facing the inletand the cellulose support facing the downstream side.

The filter media had a basis weight of 125 gsm, a caliper of 0.026″ andan air permeability of 14 cfm at 0.5″ water column. The NaCl particlefiltration efficiency was 62%. This is an improvement over the uncoatedcellulose substrate (approximately 26%). This composite had acorrugation depth of 0.012″ on the meltblown nanofiber coated side and0.016″ on the reversed, uncoated (wire) side. The mean peel strength ofthe nano fiber layer to the base substrate was 2.4 ounces per inchwidth.

13. Sample M

Sample M was prepared by forming a 5 gsm meltblown web from 0.4 micronpolypropylene fibers (Exxon PP3546 G, ExxonMobil Chemical Company,Houston, Tex.) produced from a polymer heated to 450° F. at rate of 20lbs of polymer/hr from a 35 holes per inch die blown by process airheated to 450° F. at a flow rate of 4360 lbs/hr while quenching with 55°F. air at 490 lbs/hr. The meltblown material was collected on the barecollector belt moving at 45 ft/min with a vacuum pressure ofapproximately 20 inches of water through a 7 inch wide slot. The freestanding nanofiber meltblown had a caliper of less than 0.001″, a basisweight of 5 gsm, air permeability of 150 cfm at 0.5″ water column.

The meltblown nanofiber was adhered to a corrugated support layer formedfrom a cellulose fiber containing 20% vinyl acetate resin 80% cellulosicfiber wet laid nonwoven with a basis weight of 114 gsm and an airpermeability of 16 cfm at 0.5″ water. The corrugated support layer had acorrugation channel width of 0.22″. The corrugation depth of the supportlayer was 0.022″ on the felt side to be coated, the opposite (Wire) sidehad a corrugation depth of 0.022″ as measured with the IAS LaserCorrugation Gauge.

The meltblown nanofiber was adhered to the cellulose support byapplication of a hot melt glue (Bostik M2751 adhesive) heated to 400° F.and sprayed at 410° F. at an areal weight of 6 g/m2 to the cellulosesupport and then immediately bonding the glue applied layer to themeltblown/nanofiber cellulose by contact pressure between a stainlesssteel belt used to collect the meltblown fibers and a rubber roller at anip pressure of 30 pounds per linear inch (PLI). The article was madeinto a filter element having the meltblown nanofiber facing the inletand the cellulose support facing the downstream side.

The filter media had a basis weight of 125 gsm, a caliper of 0.029″ andan air permeability of 14 cfm at 0.5″ water column. The NaCl particlefiltration efficiency was 63%. This is an improvement over the uncoatedcellulose substrate (approximately 26%). This composite had acorrugation depth of 0.016″ on the meltblown nanofiber coated side and0.018″ on the reversed, uncoated (wire) side. The mean peel strength ofthe nanofiber layer to the base substrate was 2.0 ounces per inch width.

14. Sample N

Sample N was prepared by forming a 5 gsm meltblown web from 0.4 micronpolypropylene fibers (Exxon PP3546 G, ExxonMobil Chemical Company,Houston, Tex.) produced from a polymer heated to 450° F. at rate of 20lbs of polymer/hr from a 35 holes per inch die blown by process airheated to 450° F. at a flow rate of 4360 lbs/hr while quenching with 55°F. air at 490 lbs/hr. The meltblown material was collected on the barecollector belt moving at 45 ft/min with a vacuum pressure ofapproximately 20 inches of water through a 7 inch wide slot. The freestanding nanofiber meltblown had a caliper of less than 0.001″, a basisweight of 5 gsm, air permeability of 150 cfm at 0.5″ water column.

The meltblown nanofiber was adhered to a corrugated support layer formedfrom a cellulose fiber containing 20% vinyl acetate resin 80% cellulosicfiber wet laid nonwoven with a basis weight of 122 gsm and an airpermeability of 28 cfm at 0.5″ water. The corrugated support layer had acorrugation channel width of 0.170″. The corrugation depth of thesupport layer was 0.013″ on the felt side to be coated, the opposite(Wire) side had a corrugation depth of 0.013″ as measured with the IASLaser Corrugation Gauge.

The meltblown nanofiber was adhered to the cellulose support byapplication of a hot melt glue (Bostik M2751 adhesive) heated to 400° F.and sprayed at 410° F. at an areal weight of 6 g/m2 to the cellulosesupport and then immediately bonding the glue applied layer to themeltblown/nano fiber cellulose by contact pressure between a stainlesssteel belt used to collect the meltblown fibers and a rubber roller at anip pressure of 30 pounds per linear inch (PLI). The resulting articlewas made into a filter having the meltblown nanofiber facing the inletand the cellulose support facing the downstream side.

The filter media had a basis weight of 134 gsm, a caliper of 0.021″ andan air permeability of 24 cfm at 0.5″ water column. The NaCl particlefiltration efficiency was 62%. This is an improvement over the uncoatedcellulose substrate (approximately 20%). This composite had acorrugation depth of 0.08″ on the meltblown nanofiber coated side and0.011″ on the reversed, uncoated (wire) side. The mean peel strength ofthe nano fiber layer to the base substrate was 2 ounces per inch width

15. Sample O

Sample O was prepared by forming a 25 gsm meltblown web from 0.6 micronPBT fibers (Ticona JKX) produced from a polymer heated to 550° F. atrate of 80 lbs of polymer/hr from a 35 holes per inch die blown byprocess air heated to 57° F. at a flow rate of 2500 lbs/hr. Themeltblown material was collected on the bare collector belt moving at 40ft/min with a vacuum pressure of approximately 20 inches of waterthrough a 7 inch wide slot.

The meltblown nanofiber was adhered to a support layer formed from acellulose fiber containing 20% phenolic resin and 80% cellulosic fiberwet laid nonwoven with a basis weight of 200 gsm and an air permeabilityof 2 cfm at 0.5″ water. Overall thickness was 0.029″ and corrugationdepth was 0.013″.

The meltblown nanofiber was adhered to the cellulose support byapplication of a hot melt glue (Bostik Vitel 4361B adhesive) heated to450° F. and sprayed at 450° F. at an areal weight of 8 g/m2 to thecellulose support and then immediately bonding the glue applied layer tothe meltblown/nano fiber cellulose by contact pressure between astainless steel belt used to collect the meltblown fibers and a rubberroller at a nip pressure of 35 pounds per linear inch (PLI). Theresulting structure was made into a filter media having the meltblownnano fiber facing the inlet and the cellulose support facing thedownstream side.

The filter media had a basis weight of 233 gsm, a overall caliper of0.024″ and an air permeability of 1.9 cfm at 0.5″ water column. Thiscomposite had a corrugation depth of 0.06″ on the meltblown nanofibercoated side and 0.010″ on the reversed, uncoated (wire) side. The meanpeel strength of the nanofiber layer to the base substrate was 3.5ounces per inch width.

16. Comparison Example

The comparison example 1 was prepared by forming a 5 gsm meltblown webfrom 0.7 micron polypropylene fibers (Exxon PP3546 G, ExxonMobilChemical Company, Houston, Tex.) produced from a polymer heated to 425°F. at rate of 20 lbs of polymer/hr from a 35 holes per inch die blown byprocess air heated to 435° F. at a flow rate of 3900 lbs/hr whilequenching with 55 F air at 520 lbs/hr. The meltblown material wascollected on the bare collector belt moving at 60 ft/min with a vacuumpressure of approximately 20 inches of water through a 7 inch wide slot.The free standing nanofiber meltblown had a caliper of less than 0.001″,a basis weight of 5 gsm, air permeability of 172 cfm at 0.5″ watercolumn.

The meltblown nanofiber was adhered to a corrugated support layer formedfrom a cellulose fiber containing 17% vinyl acetate resin and 83%cellulosic fiber wet laid nonwoven with a basis weight of 125 gsm and anair permeability of 32 cfm at 0.5″ water. The corrugated support layerhad a corrugation channel width of 0.170″. The corrugation depth of thecorrugated support layer was 0.015″ on the felt side to be coated, theopposite (Wire) side had a corrugation depth of 0.015″ as measured withthe IAS Laser Corrugation Gauge.

The meltblown nanofiber was adhered to the cellulose support byapplication of a hot melt glue (Bostik 4379 PVA copolymer adhesive)spray at an areal weight of 3 g/m² to the cellulose support and thenimmediately bonding the glue applied layer to the meltblown/nano fibercellulose by contact pressure between a belt used to collect themeltblown fibers and a rubber roller. The resulting article was madeinto a filter having the meltblown nano fiber facing the inlet and thecellulose support facing the downstream side.

The filter media had a basis weight of 134 gsm, a caliper of 0.027″ andan air permeability of 27 cfm at 0.5″ water column. The NaCl particlefiltration efficiency was 50%. This is an improvement over the uncoatedcellulose substrate (approximately 20%). This composite had acorrugation depth of less than 0.001″ on the meltblown nanofiber coatedside and 0.015″ on the reversed, uncoated (wire) side. This media wasused to construct an element with a pleat height of 1.13″, elementheight of 14.375″ and pleat count of 155 on a 3″ center tube (16.5pleats per inch center tube ID). The dust holding capacity was reducedby 25% at a face velocity of 300 cfm per SAE J726 protocol in comparisonto conventional media. Examining the filters and pleat packs it wasfound that the unbonded meltblown Nano fiber was blocking the filterinlets formed by the pleating knuckles adding air resistance.

This media was also used in a element with a pleat height of 0.88″,element height of 3.125″ and a pleat count of 200 around a 10″ tube (6.4pleats per inch center tube ID). The element was tested per SAE J726protocol using a face velocity of 65 cfm. With this less dense pleatedconstruction (.about.6 pleats/in vs. 17 pleats/in), dust holdingcapacity was 11% higher than conventional media.

Examples L-O demonstrated that using the method disclosed herein resultsin a corrugated filter medium having superior corrugation properties,such as corrugation depth.

C. Discussion

The following discussion provides some general observations based onrelevant data.

The fiber diameters of 100 fibers at 1000× were measured using scanningelectron microscopy (SEM). The fiber diameter was calculated (D, Log D,RMS D, D2/D) along with the geometric standard deviation to determinethe distribution of fiber diameters. The average (log D) fiber diameterswere used as a reference to characterization the different samples. Themeltblown nano fibers were considerably finer than normal meltblownfibers, approaching that of electrospun, but with a significantlybroader distribution (˜2 GSTD meltblown nanofibers vs. <1.3 forElectrospun nano fibers).

The meltblown nanofibers were considerably finer, but not as fine as theelectrospun Nano fibers.

Looking at the cross-sectional areas, the meltblown nanofiber was shownto be quite different from the electrospun nano fiber. The electrospunnanofiber had a nano fiber layer thickness of one micron to fourmicrons, whereas the meltblown nanofiber had a nanofiber layer thicknessof 17 microns to 30 microns.

For industrial cleaning applications, application of meltblownnanofibers can allow the use of a more open base material (Samples B andE), which would lower restriction and extend useful filter life, whilemaintaining and slightly increasing efficiency of dust capture. Filterlife of meltblown nanofiber coated media offers a substantial increasein operating time when compared to standard cellulose application grade(H&V FA6176).

Samples E, F and G had greater dust holding capacity than the standardapplication base material (approximately 16% to 40% improvement overstandard application grade material). It is notable that in thecomparison of Samples F and G that Sample G had a lower applied weightof meltblown nano fiber and also less dust holding capacity, suggestingthat the quantity of meltblown nano fibers plays a role in the totaldust holding capacity of the composite.

The meltblown fibers seemed to create a better, more homogenous dustcake, and the dust cake itself was easier to remove with pulsing givinga unique form of surface and depth filtration. With an open, lowdensity, meltblown structure with some depth (Samples B, D and E), dustwas formed in open funnels that are easily removed. In comparison toelectrospun nano fiber, which only has surface filtrationcharacteristics, the cleanable dust capacity might be more limited. Forstandard application grade cellulose media, the pressure rise from theaging was prohibitively high and therefore can be interpreted as havingpractically no cleanability behavior after aging. Meltblown nano fibercoatings of Sample B, D and E have shown very good retention ofcleanability behavior after ageing (more than 70% of initial).

It was clear that fine particle capture efficiency was greatly improvedby the presence of the meltblown nanofibers, as was also true for theelectrospun nanofibers over the standard application grade cellulose.The meltblown nanofiber had the unique property of added particlecapacity which lessens the pressure rise across the filter withaccumulation of fine particles and nearly doubles filter life incomparison to standard application grade cellulose. It is believed thatelectrospun nanofiber actually would decrease filter life due tocollection of fine particles at the outermost surface when the nanofiber is applied upstream and at the cellulose/nanofiber interface whenthe nano fiber layer is positioned downstream, greatly increasingpressure drop. In the case of the meltblown nanofiber composite, theparticles were collected also in the meltblown layer increasing fineparticle capture capacity.

The same observations for the heavy duty air grades can be made as forthe Auto Air grades. Differences in particle capture efficiency for theheavy duty air grades between the nanofiber coated grades to thestandard application cellulose are less dramatic due its fine porestructure and lower permeability. However, this fine base pore structurebecomes clogged with fine particles rapidly resulting in a rapidpressure rise, greatly limiting useful operating life. The applicationof meltblown nanofibers through improved particle collection greatlyextends operating life by over 300%.

The capacity of the meltblown nano fiber grades greatly exceeded that ofthe standard application cellulose and the electrospun nano fibercoated.

It should be noted that a second standard application cellulose wascompared to sample B due to the coating orientation of the cellulosebase sheet being on the more open side (felt), whereas for auto air thecoating would normally be on the wire side. Challenging the wire side(which has a finer pore structure) of any cellulose media with a duststream will reduce capacity due to the presence of fine pores. Underthese conditions, the meltblown nanofiber has a diminished effect on thefine particle capacity of the composite media.

According to the liquid filtration efficiency test, the nano fibercoated cellulose greatly improved filtration performance for cellulosemedia, whereas electrospun nanofiber gives only a temporary improvementin performance and relatively quickly loses its advantage due todegradation of the fine fiber structure. Particle capture efficiency atparticle sizes of four microns and 10 microns are improved by theaddition of meltblown nanofibers over conventional cellulose media. At aparticle size of 25 microns, particle capture efficiency was notimproved by the addition of meltblown nanofibers. The size particlesthat can be captured at 90% efficiency and 99% efficiency, respectively,is considerably finer for Sample J (5.5 microns and 8.1 microns,respectively) compared to cellulose (11.1 microns and 17.9 microns,respectively). The size particles that can be captured at 90% efficiencyand 99% efficiency, respectively, is also considerably finer for SampleJ (5.5 microns and 8.1 microns, respectively) compared to electrospunfiber (9.8 microns and 14.6 microns, respectively).

While certain embodiments have been described, other embodiments arepossible.

As an example, while embodiments have been described in which a scrim isdisposed between a substrate and a meltblown layer, in certainembodiments, the meltblown layer can be between the substrate and thescrim.

As another example, while embodiments have been described in which afilter medium includes three layers, a filter medium can optionallyinclude more layers. In some embodiments, a filter medium may have morethan one substrate, more than one intermediate layer (e.g., more thanone adhesive, more than one scrim), and/or more than one meltblownlayer. As an example, in some embodiments, a filter medium can include ameltblown layer with fibers having an average fiber diameter and asecond meltblown layer with fibers having a different average fiberdiameter. A filter medium can also include additional layers.

As a further example, while embodiments have been described in which afilter medium has one meltblown layer, a filter medium can optionallyinclude more than one meltblown layer. In certain embodiments, a filtermedium can include a meltblown layer disposed on a meltblown layer.

As an additional example, while certain methods have been described formaking a filter medium, other methods may also be used. As an example,in some embodiments, the substrate can be formed of a bicomponent film(e.g., a relatively low melting point material and a relatively highmelting point material), onto which the meltblown material is formed.Subsequently, the relatively low melting point material is heated tomelt the material (e.g., via the heat from the meltblown material and/orvia heating in an oven), followed by cooling (e.g., to room temperature)to provide a filter medium that includes the meltblown material directlybonded to the substrate. As another example, in some embodiments, thesubstrate can be formed of two layers with one layer being formed of therelatively low melting point material and the other layer being formedof the relatively high melting point material. In such embodiments, themeltblown material can be deposited on the relatively low melting pointmaterial. Subsequently, the relatively low melting point material isheated to melt the material (e.g., via the heat from the meltblownmaterial and/or via heating in an oven), and cooling (e.g., to roomtemperature) provides a filter medium that includes the meltblownmaterial directly bonded to the substrate. The materials (relatively lowmelting point material, relatively high melting point material) fromwhich the substrate is formed can be any desired material with theappropriate melting characteristics. Typically, such materials arepolymers. In some embodiments, the relatively low melting point materialcan be one of the adhesives described above (e.g., the substrate can bea film formed of a composite that includes the adhesive). Optionally, ascrim and/or additional other layers of material can be incorporatedinto the filter medium. In certain embodiments, the substrate caninclude one or more additional materials.

As a further example, while embodiments have been described in which ameltblown material is bonded with a substrate via chemical bonding usingan adhesive or mechanical bonding using ultrasonic bonding ormelting/cooling, in some embodiments, other types of mechanical bondingcan be used. Examples include stitching, sewing, hydroentangling andneedling. In some methods, such as needling and hydroentangling, themeltblown material can become intermingled with another layer (e.g., thesubstrate).

As yet another example, while embodiments have been described in whichmeltblown material is used, additionally or alternatively, othermaterials can be used. More generally, without limitation to thematerial used or the process of forming the fibers, a material withfibers having an average diameter at most 1.5 microns (e.g., at most 1.4microns, at most 1.3 microns, at most 1.2 microns, at most 1.1 microns,at most one micron), and/or at least 0.2 micron (e.g., at least 0.3micron, at least 0.4 micron, at least 0.5 micron), as measured usingscanning electron microscopy, can be used in what is described above asthe meltblown layer. In some embodiments, the material is formed usingmelt processing (e.g., a meltblown process, spun bond, extrusion andblown film extrusion). In some embodiments, the small average diametermaterial can be formed by other methods. As an example, the smallaverage diameter material can be made by taking a fiber of a relativelylarge diameter and stretching it to form the small average diametermaterial. Other methods include the “islands in the sea” and “segmentedpie” methods of forming fibers, such as described in U.S. Pat. Nos.5,783,503; 5,935,883; and 6,858,057, which are hereby incorporated byreference only to the extent that they are consistent with the remainderof the disclosure herein. In some embodiments, the material isnon-polymeric (e.g., a glass, a ceramic). For example, the material canbe a wet laid glass. In some embodiments, the substrate can be formed ofa wetlaid glass with a relatively large average diameter (e.g., at mosttwo microns, at most three microns, three microns to four microns), and,rather than a meltblown layer, the filter can include a layer of wetlaidglass fiber with a relatively small average diameter (e.g., at most 1.5microns), where the filter medium may or may not include an adhesivematerial.

As a further example, although embodiments have been described in whichthe filter medium is corrugated and/or pleated, more generally, thefilter medium can be shaped in any of a variety of desirable fashions.Such shapes are generally know in the art. Examples of shapes includedimpled, fluted, embossed and glue bead separated, bag structure ortubular structure.

Other embodiments are in the claims.

1. A method of forming a meltblown fiber web comprising: extruding apolymer melt through a die to form a polymer extrudate; impinging theextrudate with process air when forming polymer fibers from theextrudate, wherein the process air volume is greater than 2500pounds/hour-meter; and collecting the polymer fibers on a collector toform a meltblown fiber web, while applying a vacuum of at least 10inches of water, wherein an average diameter of the polymer fibers is atmost 1.5 microns.
 2. The method of claim 1, wherein the average diameterof the polymer fibers is at most 1.0 microns.
 3. The method of claim 1,wherein the average diameter of the polymer fibers is at least 0.2micron.
 4. The method of claim 1, wherein the process air volume is atleast 2750 pounds/hour-meter and at most 4000 pounds/hour-meter.
 5. Themethod of claim 1, wherein the vacuum is at least 14 inches of water. 6.The method of claim 1, wherein the vacuum is at least 14 inches of waterand at most 26 inches of water.
 7. The method of claim 1, wherein thecollector speed is at least 10 feet/min.
 8. The method of claim 1,wherein the polymer melt is extruded through a die tip having a seriesof holes to form the polymer extrudate.
 9. The method of claim 1,wherein the polymer melt is heated to a temperature of at least 350° F.in the extruder.
 10. The method of claim 1, wherein the meltblown fiberweb has a basis weight of at least 1 g/m² and at most 100 g/m2.
 11. Themethod of claim 1, wherein the meltblown fiber web has a thickness of atleast five microns to at most 250 microns.
 12. The method of claim 1,wherein the air permeability of the meltblown fiber web is at least 20CFM to at most 500 CFM.
 13. The method of claim 1, further comprisingforming a filter medium comprising the meltblown fiber web.
 14. Themethod of claim 13, wherein the filter medium includes a substrate thatsupports the meltblown fiber web.
 15. The method of claim 1, wherein theprocess air comprises heated air on sides of the die tip where thefibers are formed.
 16. The method of claim 1, wherein the process airhelps attenuate the polymer fibers to a final fiber size.